An asphaltene content in heavy hydrocarbon oils is not only an indication of combustibility and storage stability of heavy hydrocarbon oils but also an important factor greatly influencing catalytic activity in a direct disulfurization process. Therefore, it is required to carry out determination of asphaltene content in heavy hydrocarbon oils rapidly and precisely from consideration of product control and process control.
Determination of asphaltene content has been commonly carried out based on a method of The Institute of Petroleum (IP 143, hereinafter referred to as IP method). IP method comprises dissolving a sample in a prescribed amount of warm n-heptane, filtering the resulting mixture using a filter paper, washing an insoluble matter collected by filtration with heptane at reflux in a Soxhlet's extractor, extracting the insoluble matter with toluene in the extractor, and determining the extracted soluble matter. However, since the IP method involves complicated operations and requires much time as long as 9 hours for analysis, it has been partly replaced by a method of Universal Oil Product Co. (UOP 614/80, hereinafter referred to as UOP method), in which a sample dissolved in a prescribed amount of warm n-heptane is filtered through a membrance filter and the insoluble matter collected on the filter is determined as an asphaltene content. The UOP method, however, still requires about 4 hours for analysis, and the measured values do not agree with those obtained by IP method. Accordingly, it has been demanded to develop a simple and rapid method of asphaltene determination which gives measured values in good agreement with IP values.
Methods of rapid determination of asphaltene content so far proposed include (1) Ono method (Tastuo Ono, J. of Japan Petrol. Inst., Vol. 14, No. 9, 504 (1971)), (2) absorptiometric methods (Tsutomu Kaibara et al., J. of Japan Petrol. Inst., Vol. 23, No. 3, 178 (1980)), and (3) hydrogen flame ionization detection thin-layer chromatographic methods (FID-TLC) (Marc-Andre Poirier et al., J. of Chromatographic Science, Vol. 21, No. 7,331 (1983) and Yojiro Yamamotlo et al., J. of Japan Petrol. Inst., Vol. 27, No. 3,269 (1984)).
The Ono method comprises the same procedures as IP method except for omitting the toluene extraction, and the time required for analysis and measured values are substantially equal to those of the UOP method.
The hydrogen flame ionization detection thin-layer chromatographic method by Yamamoto et al. comprises spotting a sample solution on a silica gel thin layer rod, developing the sample with a solvent, e.g., toluene, to separate asphaltene, and determining the asphaltene content by means of a flame ionization detector. Although this method succeeded to furnish measured values in correlation with IP values and to reduce the time required for analysis to 30 to 60 minutes per 10 samples, it has disadvantages in that an analyst should always scan the system throughout measurement and that analysis precision greatly depends on development conditions, resulting in poor reproducibility.
The absorptiometric method by Kaibara et al. comprises dissolving a sample in n-heptane, measuring absorbance of the solution at a wavelength of 700 nm by means of a spectrophotometer, further measuring absorbance of a filtrate obtained by filtration of the solution at a wavelength of 700 nm, and obtaining an asphaltene concentration from a difference in absorbance of the solution between before and after the filtration. According to this method, the time required for analysis is reduced to about 30 minutes. However, the operation of filtration is complicated, and the measured values, though correlating with IP values, has a coefficient of correlation of 0.979, that is lower than a generally acceptable coefficient of correlation, i.e., not less than 0.99.
Another problem is that the upper limit of determination range is 3% by the conventional methods. Incidentally, an asphaltene content in heavy hydrocarbon oils, which depends on a kind of crude oil and cut fraction, is generally 1 to 5% in long residue and 5 to 30% in short residue. In addition, tar sand oil contains such a large amount of asphaltene content as 15 to 20%. In Japan, a research and development relating to techniques for lightening a heavy hydrocarbon oil has widely advanced from a view point of recent oil supplying circumstances. Thus, it has been desired to provide a method for rapid determination of asphaltene content as wide as possible.
A method and device of the present invention is developed to resolve various problems of the conventional asphaltene content determination means. The method of the present invention can determine asphaltene content at a wider range concentration and more rapidly as compared with the conventional methods by combining a means of sample preparation for precipitation of asphaltene and a method for two-wavelength absorbance detection connected thereto. The device of the present invention provide a determination device composed of a two-wavelength absorbance detector to determine asphaltene content by the afore-mentioned means, an automatic sample feeder connected thereto, and a microcomputer and make it possible asphaltene determination by which a number of samples can be analyzed surely and rapidly without requiring much labor.